Help finding the date for which my curve fit predicts 5% of positive daily tests.

I'm im about just a done with a project which analyzes a positive COVID-19 test in Oregon but im running into a problem thinking about how to create a formula which will find where the curve predicts 5% of positive daily tests.

%Prediction 150 days from data
npredict=n+100;
x=1:npredict;
a=curve1.a;
b=curve1.b;
predict=(1./x/a/sqrt(2*pi).*exp(-(log(x)-b).^2/2/a^2))*dataPositiveL;

% Target: find date for which curve fit predicts 5% of positive  daily tests
daytarget=predict*.05
[err idx]=min(abs(predict-daytarget))

% Use date algebra to find the date
t0=datetime(2020,3,4);
daytarget = t0+idx

I think I just dont understand the wording of what is being looked for.

[Rik]

A copy of this question in case it get deleted too:

Help finding the date for which my curve fit predicts 5% of positive daily tests.

I'm im about just a done with a project which analyzes a positive COVID-19 test in Oregon but im running into a problem thinking about how to create a formula which will find where the curve predicts 5% of positive daily tests.

%Prediction 150 days from data
npredict=n+100;
x=1:npredict;
a=curve1.a;
b=curve1.b;
predict=(1./x/a/sqrt(2*pi).*exp(-(log(x)-b).^2/2/a^2))*dataPositiveL;

% Target: find date for which curve fit predicts 5% of positive  daily tests
daytarget=predict*.05
[err idx]=min(abs(predict-daytarget))

% Use date algebra to find the date
t0=datetime(2020,3,4);
daytarget = t0+idx

I think I just dont understand the wording of what is being looked for.